This invention relates to metal dithiophosphates, a process for their manufacture and lubricating oil compositions containing said metal dithiophosphates. More specifically, it relates to a process for the manufacture of zinc, barium, cadmium, magnesium or nickel dithiophosphates.
It is well known that various additives can be added to lubricating oils in order to improve various oil properties and to make a more satisfactory lubricant. Antiwear agents are intended to decrease wear of machine parts. Wear inhibitors for incorporation in motor oils and industrial oils are finding greater use as a result of greater stress placed on moving parts in high performance engines. Numerous additives have been developed for use in such oil compositions to improve the lubricating characteristics thereof and thereby to lessen the wear of the moving parts.
Metal diaryl and dialkyl dithiophosphates, especially zinc dithiophosphates (ZOP), have long been used as antiwear additives and antioxidants in hydraulic oils, motor oils, automatic transmission fluids and the like. In the manufacture of such metal dithiophosphates, dithiophosphoric acid is commonly neutralized with a metal base, such as zinc oxide. This neutralization step does not take place readily and commonly a large excess of the base is used in conjunction with a neutralization promoter, generally an acidic promoter. Sometimes the use of acidic promoters such as nitric acid can lead to undesirable side effects such as haze or instability. In many cases the neutralized product is difficult to filter and has a dark color.
It is an object of this invention to provide an improved process for the manufacture of metal diaryl and dialkyl dithiophosphates.
It is an object of this invention to provide a process for the manufacture of metal dithiophates wherein low excess metal base is required for the neutralization of dithiophosphoric acids.
It is an object of this invention to provide a process for the manufacture of metal diaryl dithiophosphates wherein the neutralized product does not suffer undesirable side effects caused by an acidic promoter.
It is further an object of this invention to provide a highly effective antiwear and antioxidant additive for use in lubricating oils.